This invention relates generally to marine riser conduit section coupling means which are adapted to withstand high riser tension and bending loads in deep subsea well drilling and production operations by preventing stress concentrations. More specifically, the present invention relates to a construction of coupling means for optimizing the distribution of tension and bending loads through the coupling in a practical manner when employed in association with a marine riser conduit run in sections from a floating vessel to a very deep subsea well.
Heretofore it has been common to run marine risers from floating vessels or platforms to subsea well heads for various drilling and production operations. The marine riser comprises a plurality of conduit sections which are assembled together on the vessel or platform and run by known means from the vessel down to the well. As deeper and deeper well drilling and production operations have been undertaken, the tension and bending loads imparted to the riser and its conduit sections have been increasing. It has been found that the heretofore conventionally used coupling means for fastening successive riser conduit sections together may be inadequate to withstand these very high loads by allowing the production of stress concentrations. Specifically, prior coupling means which employ a plurality of movable dog means on one mating member and a peripheral groove on the other mating member tend to concentrate the stresses imparted to the coupling under these tension and bending loads in a central area of the coupling where the movable dog members and mating groove means are provided, respectively.
It has therefore been recognized that an improved coupling means is needed for the specific situation of very deep well drilling and production operations in association with a marine riser run in successive joined sections to a very deep well head.